The Belgian Government in London (, ), also known as the Pierlot IV Government, was the government in exile of Belgium between October 1940 and September 1944 during World War II. The government was tripartite, involving ministers from the Catholic, Liberal and Labour Parties. After the invasion of Belgium by Nazi Germany in May 1940, the Belgian government, under Prime Minister Hubert Pierlot, fled first to Bordeaux in France and then to London, where it established itself as the only legitimate representation of Belgium to the Allies. Despite no longer having authority in its own country, the government administered the Belgian Congo and held negotiations with other Allied powers about post-war reconstruction. Agreements made by the government in exile during the war included the foundation of the Benelux Customs Union and Belgium's admission into the United Nations. The government also exercised influence within the Belgian army-in-exile and attempted to maintain links with the underground resistance. Background Politically, Belgian politics had been dominated in the interwar period by the Catholic Party, usually in coalition with the Belgian Labour Party (POB-BWP) or the Liberal Party. The 1930s also saw the rise in popularity of Fascist parties within Belgium; most notably Rex which peaked at the 1936 election with 11% of the vote. From the early 1930s, Belgian foreign and domestic policy had been dominated by the policy of neutrality; leaving international treaties and alliances and attempting to maintain good diplomatic relations with Britain, France and Germany. Despite this policy, Belgium was invaded without warning by German forces on 10 May 1940. After 18 days of fighting, the Belgian military surrendered on 28 May and the country was placed under the control of a German military government. Between 600,000 and 650,000 Belgian men (nearly 20% of the country's male population) had been mobilized to fight. Unlike the Netherlands or Luxembourg, whose monarchies went into exile alongside the government, King Leopold III surrendered to the Germans alongside his army – contrary to the advice of his government. In the days before his surrender, he allegedly attempted to form a new government under the pro-Nazi socialist Henri de Man though this was never realized. He remained a prisoner of the Germans, under house arrest, for the rest of the war. Although the government briefly attempted to negotiate with the German authorities from exile in France, the German authorities passed a decree forbidding members of the